As is well known, a plurality of semiconductor circuits, are formed in large semiconductor wafers. The circuits are typically arranged on the wafer in rows and columns separated one from the other by regions known as kerfs. Once the circuits are formed in the wafer; metallic connections are provided on the surface of each circuit; the circuits are then separated one from the other; each circuit is then mounted on a nonconductive base or substrate such that it may be further handled or provided with a protective cover.
Such nonconductive bases or substrates are typically divided out of a larger, thin sheet of a rigid insulating material, such as ceramic, that has arranged on one surface thereof a plurality of individual wiring blocks. Each wiring block on the sheet comprises a wiring path and connections designed for the semiconductor chip to be placed thereon. These wiring blocks are formed on the insulating sheet in rows and columns that are separated one from the other by isolating regions known as kerfs.
A respective semiconductor chip is then electrically bonded to each respective block and the sheet is then divided in each kerf to singularize the blocks one from the other. In this way, each chip is provided with a respective substrate or base that is suitable for receiving a protective cover over the chip.
An early method of individualizing or singularizing such substrates from such a larger sheet consisted of sawing the insulating sheet in the kerf areas between the blocks. This method was found to be very slow and caused fine debris to be deposited on the surface of the blocks requiring follow-up cleaning steps. Moreover such cleaning steps were often ineffective in removing debris lodged beneath chips that were mounted on each block prior to the sawing action.
A later method consisted of scribing, on the sheet, a first set of scribed lines in the row kerfs and a second set of scribed lines in the column kerfs, which are perpendicular to the first set of scribed lines to create a plurality of cross hatched lines on the sheet surface. Using this process, the scribe lines enclose a plurality of defined enclosed regions on the substrate surface. A printed circuit wiring block is then formed in each scribe defined region and a respective chip is mounted on each printed circuit block. Next the chip carrying scribed sheet is placed on an elastic base and the sheet is fractured along the scribed lines by passing a roller over the sheet in a first direction parallel to the first set of the scribed lines and then passing the roller over the sheet in a second direction that is parallel to the second set of scribed lines, and at right angles to the first direction. This method, however, proved unsatisfactory because of variations in the force exerted on the roller and in the elasticity of the base, causing fractures to occur in the sheet in regions other than along the scribed lines. Still further, because chips had been mounted on the sheet prior to passing the roller over the surface of the unit, the rolling action was found to cause deformations and/or breaking of the conductive bonds between the chips and the underlying wiring blocks on the ceramic substrate. All of these difficulties resulted in excessive failure rates.
Another method employed a machine in which the chip carrying scribed sheet was placed against a convex die and a steel band was drawn against the chip mounted sheet, forcing the sheet against the die and causing the sheet to fracture along the first set of scribed lines, and then turning the partially broken substrate ninety degrees to fracture the substrate on the first set of lines. This machine also had difficulties associated with it for when used on a production line the tension on the band was found to be difficult to control and if the tension was even just slightly excessive, the blocks themselves were broken or cracked in undesired regions. Also the movement of the band across the surface of the chips mounted on the blocks often caused deformations and/or breaking of the conductive bonds between the chips and the underlying wiring blocks again resulting in undesirable losses.
A further method of subdividing such a scribed sheet carrying chips thereon used two sets of mating convex and concave arched dies positioned inline. The direction of the curves of the dies of the second set being positioned at a right angle with respect to the direction of the curves in the first set. The scribed sheet, to be subdivided, is mounted on an adhesive tape passing between both sets of dies. The sheet, is then positioned between the dies of the first set so that the convex die could be moved to force the scribed sheet against its mating concave die to break the sheet along a first set of the crosshatched scribed lines, following which the convex die was retracted, the tape moved between the second set of dies and the process repeated to fracture the sheet along the second set of scribed lines. In this arrangement each die in a set must be exactly positioned with respect to its mating die, for any misalignment of the dies or improper spacing between the dies when closed can result in either un-separated portions of the sheet or breakage of the sheet in undesired areas or breaking or distortion of the chip to block bonds. Further it was found that the first set of mating dies could cause a distortion in the tape resulting in an inappropriate shifting and misalignment of the sheet under the second set of dies. These problems also resulted in undesirable failure rates. Because of these difficulties a better mechanism and process for subdividing or singularizing a chip carrying sheet has long been sought.